A Reconfigurable Fractional-Conversion-Ratio Charge Pump for Energy Harvesting Applications

In this paper, a fully integrated reconfigurable charge pump (CP) is presented. In energy harvesting applications, the input voltage can have large variations due to change in the environmental conditions, thus the CP has to be highly reconfigurable to support a wide range of input voltages together with expected load current variations. The proposed CP offers a fractional conversion ratio in order to optimize the overall system efficiency. The analysis of the CP in terms of output resistance, optimum number of stages for a given output voltage, and efficiency is performed. A design example is shown for a 5-stage CP using a UMC 180nm CMOS technology. The CP has a programmable conversion ratio from 1.25 to 5 in steps of 0.25 to support an input voltage from 0.3V to 1.2V and an output voltage of 1.5V. The implementation uses a total on-chip pumping capacitor of 2.5nF and achieves an efficiency of more than 73% across the whole input range at a load current of 1mA.